The semiconductor manufacturing industry has achieved remarkable success in reducing manufacturing costs. As a result, the cost of most electronic products continues to drop, even as these products provide ever greater capabilities and value. In the past, some of the lower manufacturing costs have been achieved by running large lots of wafers in large batch processing machines. However, the semiconductor manufacturing industry is now tending to move away from batch processing and toward single wafer processing. Consequently, techniques for speeding up single wafer processing are needed.
A significant productivity challenge in semiconductor device manufacturing is process waiting time. For every minute that a micro-electronic substrate or wafer undergoes processing, the wafer may be completely idle for 20-30 minutes or more, while waiting for the next process to begin. Cycle-time is the total time required for a wafer to move through the entire manufacturing process. Reducing cycle time can allow device manufacturers flexibility to adapt product type to rapidly changing market demands. Wafer lot size is the size of the lot or batch of wafers moving as a group through the manufacturing processes. Currently, a common wafer lot size is 25, i.e., the wafers move through the manufacturing facility or fab in groups of 25 (typically within a carrier capable of holding up to 25 wafers). At each tool or station, the carrier must wait until the entire lot of e.g., 25 wafers is processed. If, on the other hand, the lot size is reduced to say 5 wafers, waiting time and cycle time can be significantly reduced. The overall inventory of wafers moving through the fab can also be reduced. Both of these factors reduce manufacturing costs.
Although reducing wafer lot sizes from 25 wafers per carrier to say five wafers per carrier may conceptually be a relatively simple transition, in the real world it creates difficult engineering challenges. Going from 25 to 5 wafers per carrier requires moving the same number of wafers through the fab, but using five times more individual carrier movements. Apart from simply moving carriers faster, other factors, such as carrier storage and waiting locations, carrier access, carrier movement patterns, etc. can affect ultimate manufacturing costs.
In addition, even with current technology, when specific process times are relatively short, say for example, less than 2 or 3 minutes per wafer, the processing systems can often process wafers more quickly than the wafer transport systems in the fab can deliver wafers to the processing systems. Consequently, the processing systems are often processing wafers at rates below their maximum processing capability. As a result, manufacturers are not able to achieve all of cost savings that such processing systems can offer.
Accordingly, improved systems and methods are needed.